Thermally operated electrical disconnect device



Aug. 3, 1965 J. G. BARAN ETAL 3,198,914

THERMALLY OPERATED ELECTRICAL DISCONNECT DEVICE Filed April 18, 1962 3,198,914 TFERWLLY GFERA'ED ELECTRICAL DESCGNNECT DEVESE Joseph G. Earan, Northbrook, and Albert E. Feinberg, Chicago, Ell., assignors to Advance 'lfransiormer Co., Chicago, Ill., a corporation of Illinois liiiied Apr. I8, 1962, Ser. No. 188,323 7 Claims. (Cl. Zitti-142) This invention relates generally to a thermal disconnect means for electrical circuits and more specically is directed to a particular type of thermal disconnect means for use especially in connection with ballasts for gaseous discharge devices.

The thermal disconnect structure of the invention comprises an electrical link adapted to be interposed in the energizing circuit of a ballast. A ballast, as is known, is usually an electromagnetic apparatus adapted to be connected to an electric line for use in providing the ignition voltage and power for operating gaseous discharge devices such as, for example, .uorescent lamps, Usually the ballast is formed of a transformer and capacitors disposed in a canister and potted with a potting compound, the electrical leads extending out of the canister for connection into a circuit.

The thermal disconnect means of the invention is intended to open the energizing circuit when the temperature within the ballast exceeds approximately 125 centigrade. rl`his is just prior to the liquifying of the potting compound whereby to prevent same from running out of the canister, ruining the fixture and causing damage to property and personnel.

The primary object of the invention is to provide a thermal disconnect apparatus of simple design and low cost which is intended to be made of relatively small size and disposed completely within the interior of the canister in the potting compound.

Another object of the invention is to provide thermal disconnect means which includes a soldered joint maintaining in connection a pair of wires which are prestressed to move away from one another but are held together by a low melting point solder whereby, when the melting point of the solder is reached, lateral movement of the connected wires will occur, this movement being in a direction carrying the wires away from one another thereby electing a substantial separation between wires and alleviating the possibility of the connection accidentally being remade.

A further object or" the invention is to provide a structure of the character described in which the wires are inserted in a small housing or block having channels or slots arranged at opposite ends thereof directing the wires away from one another so that the wires are pre-stressed to have their ends separate when the soldered joint thereof is melted.

Many other objects will appear as the description of the invention proceeds in connection with which preferred embodiments are shown in the accompanying drawings.

In the said drawings:

FIG. l is a perspective view of a pair of metal strip members adapted to be soldered together and showing the ends of the same bent for purposes of pre-stressing the same.

FIG. 2 is a sectional view through a small container or block showing the disposition of the wires or metal strips of FG. l while the thermal disconnect apparatus is in use and showing in broken lines the disposition of the wire ends if the soldered joint is melted.

FIG. 3 is a perspective view of a pair of straight wire or metal strip members soldered together for use in thermal disconnect apparatus.

FIG. 4 is a top plan view of a container or block in E, l 98 ,9 l d Patented Aug. 3, i965 which the wire elements of FIG. 3 are disposed in prestressed relationship, the cover member being removed.

FIG. 5 is a view similar to that of FIG. 3 but of a modiiied form of the invention.

FIG. 6 is an exploded sectional View through a block or small housing in which the joined wires of the invention are adapted to be disposed in a pre-Stressed arrangement.

FIG. 7 is a vertical sectional viewl through the assembled housing or block of FIG. 6 showing the arrangement of the apparatus in use.

Referring now to FIG. l and FIG. 3, the thermal disconnect apparatus is required to include an electrical link which is adapted to be melted when the temperature in the ballast exceeds a predetermined value such as, for example, centigrade. As seen, the link will comprise a pair of hat metal strip or wire members, such as, for example, itl and 12 in FIG. l or 14 and 16 in FIG. 3. These flat strips may be formed of any suitable material such as copper, bronze, silver or the like, not readily adapted to melt. For example, the strips may be about 1/16 of an inch wide and .010 to .02.0 of an inch thickness.

Each of the wire strips has a free end such as 18 and 2i) in FIG. l and 22 and 24 in FIG. 3. These free ends are preferably dipped in low melting point solders such as, for example, a bismuth-tin-indium composition of suitable characteristics. In FIG. l, the free ends are shown covered with the solder at 26 and 2b. Actually it is only necessary that there be a small spot of solder on the juxtaposed facing ends of the strip members. These ends are then soldered together by resistance welding or other suit- .able technique thereby providing an intermediate soft meltable solder coupling as, for example, that shown at 3i? in FIG. 3 and at dit in FiG. 2.

The two strip or wire elements I@ and l2 in FIG. 1 are pre-bent as at 32 and 34 so that in order to solder the ends together, it will be necessary to strain the ends I8 and 2t) in a direction tending to straighten the wire members It) and I2. In FIG. 2, the resulting link designated generally 36 is shown with the soldered coupling di? formed between the ends 1S and 2li. It will be appreciated that, although the link 36 appears to be rectilinear or nearly so, the ends le and 2d are pre-stressed, and if the soldered coupling 49 should melt, the free ends I8 and 26 will try to assume their original coniiguration as indicated by the broken line portions 1S and 20'. Obviously, these free ends will move apart a very substantial distance providing thereby a substantial break in the link 36.

The link 36, as shown in FIG. 2, is disposed in a small block or open top container 42 of plastic or other insulating material to prevent the potting compound from running into the interior and interfering with the operation or" the thermal disconnect device. The ends of the block or container d2 are slotted to provide channels at i4 and 45, and the wire strips I@ and l2. are rrnly held in the slots or channels so that the body of each strip will extend straight through the slot without lateral wobbling. In this manner, the maximum of movement of the free ends l and Ztl will occur when the soldered coupling d@ separates. A suitable cover is intended to be secured over the top of the container 42.

The link 4S of FIG. 3 is made of rectilinear strip or Wire members I4 and i6. In this case, the container or block Si? has end slots 52 and 5d which may be characterized as pass-through slots for receiving the ends of strips Id and l5 threaded therethrough. The said slots are sc directed as to place the desired stress upon the strips M and Id, biasing them to separate if they can. It will be noted that the slot 52 is substantially at right angles to the left-hand wall while the slot 54 is at a substantial angle relative to the right-hand wall. The strip 24 is, therefore, directed downwardly and to ados,

the left in the View while the strip 2,2, is directed rectilinearly to the right in the View. The end 22 is biased to move to the position Z2 shown in broken lines While the end 24 is biased to move to the position 24 shown in broken lines. When the coupling 30 melts, the movement will occur separating the free ends by a substantial amount.

FIG. 5 is similar to FG. 4 except that the slots 52 and 54 are substantially parallel one to the other while being oblique relative the end walls and therefore a larger stress is placed upon the wire or strips 14 and lo. The strip 14 in FlG. 5 is directed upward and to the right out of the slot 52 as viewed while the strip 16 is directed downward and to the left by the slot 54 so that when the coupling Si? melts, these ends will assume the positions shown by the broken lines ld lr6'.

ln FEGS. 2, 4 and 5, one may consider that the views are actually top plan views o' open containers which will be covered by a rectangle of some i'iberboard or other insulating material and taped closed. The slots are, therefore, merely cnt in the end walls. ln FEiG. 6, however, the container or housing 60 is formed of two parts, probably molded, the bottom part having end walls provided with slots 6?. and 64 adapted to have the link 4S laid flat upon these grooves. A cover member has male projections and adapted to tit the grooves 62 and 64 respectively and thereby clamp the wire strips 14 and le in place. After this cover member, designated 74B is properly located, a few turns of adhesive tape such as shown at 72 in EEG. 7 maintains the apparatus in assembly. As soon as the link coupling 3th melts, the free ends will tend to separate as shown Vat Z2' and 24.

It is believed that the invention has been fully described such asfto enable those skilled in this art to understand and practice the same. Variations are capable of being made without departing from the spirit and scope of t.-e invention as set rorth in the appended claims.

What it is desired to secure by Letters Patent of the United States is:

1. A thermally operated electrical disconnect device comprising in combination a hollow housing having a pair of opposite side walls and a link extending out ot the housing through said opposite side walls and consisting of a pair of electrically conductive elements connected iriterior of the housing by a low melting point solder connection, at least one of said side walls having a passthrough slot formed therein and the respective element free end being tightly threaded Vthrough said slot, said pass-through slot being slanted relative to the side Wall so as to direct the element to assume a condition upon melting of the solder connection disposed in a plane divergent from the plane occupied by the other conductive element of the link.

2. The structure as claimed in claim l in which a pass through slot is formed in the other opposite side wall to accommodate the other element free end therethrough.

3. The structure as claimed in claim 1 in which the y other opposite side wall has a second slanted slot formed tliih and the other conductive element free end is likewise'threaded tightly therethrough, the pair of elements assuming a condition upon melting of the solder connection disposed in substantially parallel planes.

A thermally operated electrical disconnect device for a gaseous discharge ballast which includes a canister having the ballasting components immersed in potting compound therein and the disconnect device being disposed within the canister in heat exchange relationship with said ballasting components and electrically connected thereto, said disconnect device comprising a hollow housing having a pair of opposite side Walls and a link formed oi a pair of electrically conductive elements connected at adjacent ends inside of the housing by means of a low melting point solder connection, said link extending out of the housing through said opposite side walls, at least one of said side walls having a pass-through slot formed therein and the respective element free end being tightly threaded through said slot, said slot being slanted relative to the side wall to direct said element to assume a condition upon melting of the solder connection disposed in a plane divergent from the plane occupied by the other element of said link.

5. VA thermally operated electrical disconnect device for a gaseous discharge ballast which includes a canister having the ballasting components thereof immersed-in vheat conductivel potting compound and the 'disconnect device being disposed within the canister and electrically connected to said ballasting components, said disconnect device comprising link formed of a pair of electrically conductive elements parallel arranged and connected at one ot the ends thereof by a low-melting point solder connection, a hollow housing having a pair of opposite side walls and enclosing the pair ot connected ends with the free ends of said elements extending exterior of said housing, at least one of said side walls having a pass through slot formed therein receiving one of said free ends therethrough, said pass through slot being slanted relative to the plane of the housing positively to direct he connected ends positively to spring apart to a normal divergent relation upon melting of the solder connection, said element assuming a position disposed in a plane coplanar with the plane occupied by the slot.

o. The structure as claimed inV claim 5 wherein a second pass-through slot is provided to accommodate the other free end of the link.

7. The structure as claimed in claim 6 wherein the slots lie in co-directional planes.

References Cited by the Examiner UNlTED STATES PATENTS 295,760 3/84 Hill 20G-142 888,381 5/08 Andrews et al. ZOO-117 1,406,434 2/22 Baker 20G-132 1,438,609 12/22 Perkins 200-117 2,457,941 1/49 Szabo 200--142 2,759,065 8/56 Moeller 200--131 FOREIGN PATENTS 678,202 7/ 39 Germany. 763,167 12/56 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. 

1. A THERMALLY OPERATED ELECTRICAL DISCONNECT DEVICE COMPRISING IN COMBINATION A HOLLOW HOUSING HAVING A PAIR OF OPPOSITE SIDE WALLS AND A LINK EXTENDING OUT OF THE HOUSING THROUGH SAID OPPOSITE SIDE WALLS AND CONSISTING OF A PAIR OF ELECTRICALLY CONDUCTIVE ELEMENTS CONNECTED INTERIOR OF THE HOUSING BY A LOW MELTING POINT SOLDER CONNECTION, AT LEAST ONE OF SAID SIDE, WALLS HAVING A PASSTHROUGH SLOT FORMED THEREIN AND THE RESPECTIVE ELEMENT FREE END BEING TIGHTLY THREADED THROUGH SAID SLOT, SAID PASS-THROUGH SLOT BEING SLANTED RELATIVE TO THE SIDE WALL SO AS TO DIRECT THE ELEMENT TO ASSUME A CONDITION UPON MELTING OF THE SOLDER CONNECTION DISPOSED IN A PLANE DIVERGENT FROM THE PLANE OCCUPIED BY THE OTHER CONDUCTIVE ELEMENT OF THE LINK. 